In the context of firearms, a magazine is an ammunition storage and feeding device within or attached to a repeating firearm. The magazine functions by moving the ammunition cartridges stored in the magazine into a position where the cartridges are loaded into the chamber of the firearm. In order for fresh rounds of ammunition to be reloaded to the firearm reliably, each ammunition cartridge needs to be in a specific angle and position aligned with the firearm barrel so that it can be rammed into the barrel by the firearm action devices, e.g., the rifle bolt or handgun slides. To ensure such feeding process proceeds smoothly, the firearm magazine is designed to provide each round of ammunition with full support within the magazine. FIG. 3 illustrates a prior art firearm magazine 10. As shown in FIG. 3, a spring inside the magazine pushes the ammunition against the magazine lip 11 securely so that the ammunition will align axially with the barrel at the designed angle and position.
For the ease of ejection after firing, ammunition cartridges, especially rifle cartridges, have various tapering design on the casing. Due to the material used for the casing, some ammunition cartridges have larger tapering angle than others. There is one dubbed as 7.62×39, also known as M43 or 762 Russian, which has one of the largest case tapering. Another popular caliber, which is dubbed as 223 Remington, has one of the smallest case tapering. FIG. 4 illustrates an M43 ammunition 20. FIG. 5 illustrates a 223 Remington ammunition 30. As shown in FIGS. 4 and 5, the casing 22 of the M43 ammunition 20 and the casing 32 of the 223 Remington ammunition 30 have different tapering angles. FIG. 6 illustrates how the M43 ammunition cartridges are stacked inside a magazine in order to maintain full support of each ammunition cartridge. FIG. 7 illustrates how the 223 Remington ammunition cartridges are stacked inside a magazine in order to maintain full support of each ammunition cartridge. As shown in FIGS. 6 and 7, given the tapering angle of the casing, the stack of M43 ammunition cartridges and the stack of 223 Remington ammunition cartridges appear to have a “bent” shape although the stack of M43 ammunition cartridges has a more pronounced “bent” shape given the relatively larger tapering angle of the M43 ammunition casing. Accordingly, the design of the magazine may need to adopt the “bent” shape. FIG. 8 illustrates an AK style magazine that is a banana shaped magazine. There is, however, one disadvantage associated with the kind magazine as that shown in FIG. 8. As the whole magazine has a banana shape, it has to be mounted onto a firearm with a rotational action. As a result, it is not easy to drop such a magazine by its own weight when the magazine is empty.
On the contrary, rifles such as AR15 use a STANAG magazine that utilizes a straight-bent-straight design so that the end that has the feeding lip has a straight portion and can be inserted into the rifle's straight magazine wall. FIG. 9 illustrates such a STANAG magazine. When the magazine catch is released, the magazine can be dropped out of the rifle by its own weight. This allows the firearm operator to insert a loaded magazine back into the firearm with relatively less time compared to the case with the AK47 style magazine. Although the time difference may be seconds or fractions of a second, such time difference could mean a difference of life and death in the battle field.
However, such straight-bent-straight design has problems. One problem is that ammunition cartridges of different calibers have different rim diameters (the diameter of the casing near the bottom area, where the diameter is the biggest, which is called “rim”).
To stack the ammunition cartridges efficiently inside of the magazine, the ammo should be staged in the way shown in FIG. 10. This way, the ammunition cartridge is supported by the interior of the magazine groove, and by each other ammunition cartridge, tightly. However, for ammunition cartridges of other calibers having a smaller rim diameter, the minimum distance between the groove interior may not be able to support each cartridge and the support between each cartridge is no longer certain. FIG. 11 shows one of the possible positional relationships between each cartridge. Compared to what is shown in FIG. 10, the relative position of ammunition cartridges between each other inside the magazine wall can be altered. FIG. 12 shows another possibility of ammunition cartridge stacked inside of the magazine, which is a non-stable scenario. Movement of the magazine during the usage will likely shift the ammunition inside to other configurations. Such shifting may cause jam of the ammunition, and/or other malfunctions, during firing. For example, when ammunition cartridges with a smaller rim diameter are stacked in the magazine that is suitable for large rim diameters, as shown in FIG. 11, the ammunition cartridges may jump out of the magazine lip by themselves, due to the uncertain forces acted on each individual ammunition cartridge. This not only affects the reliable storage function of the magazine, it will also introduce jam that is hard to be cleared.
As AR15 rifles are among the most popular rifles in the civilian market, ammunition cartridges of different calibers are available for the AR15 rifles. Consequently, ammunition cartridges with casings of various tapering angles and rim diameters have to cope with the straight magazine wall design of the AR15 rifle.